Electronic ignition



A ril 18,1961

B. H. SHORT ELECTRONIC IGNITION Filed Sept. 12, 1958 INVENTOR.

Brooks H. .Shon

/ His A/fo r ney 2,980,093 Patented Apr. 18, 1961 ice ELECTRONICIGNITION Brooks H. Short, Anderson, Ind., assignor to General MotorsCorporation, Detroit, Mich, a corporation of Delaware Filed Sept. 12,1958, Ser. No. 760,713

4 Claims. (Cl. 123-148) This invention relates to electronic ignitionsystems and is an improvement of the circuit disclosed and claimed inapplication S.N. 561,487, filed January 26, 19 56, and now Patent2,846,992.

In the above-mentioned patent, an electronic ignition system isdisclosed and claimed which includes an electronic switch connected incircuit with the primary winding of an ignition coil. The power supplyof the system includes a plurality of cold cathode tubes and a vibrator.

Although the circuit of the above-mentioned patent has worked well, ithas been found that the expected life of this circuit is limited becauseof the limited life of the cold cathode tubes and the vibrator. The lifeof the cold cathode tubes are limited because every time the tubeconducts, a pulse of current flows and some of the active material ispulled. out of the cathode. The vibrator has a limited life because itusually has at least two sets of moving contacts that are subject todestruction by arcing and mechanical forces.

In contrast to the above-described electronic ignition circuit, it is anobject of this invention to provide an electronic ignition circuit thathas a longer expected life and which is more eflicient in operation thanthe circuit of the above-mentioned patent and any other heretofore knownelectronic ignition circuits.

A more specific object of this invention is to provide an electronicignition system that includes an electronic switch for controllingcurrent flow through the primary winding of an ignition coil and whereinthe power supplied to the primary winding is derived from a circuit thatincludes a transistor oscillator and a plurality of p-n junctionsemi-conductor rectifiers. By employing the transistor oscillator, thesubject vibrator contacts are eliminated, thus greatly prolonging theexpected life of the circuit. The use of p-n junction diodes such assilicon diodes also greatly prolongs the expected life of the ignitioncircuit as these diodes have very nearly an unlimited expected life.These diodes also increase the efiiciency of the ignition circuit as thevoltage drop across this type of diode in the current carrying directionis much less than that of a tube.

Another object of this invention is to provide an electronic ignitioncircuit that includes a transistor oscillator and a transformerconnected therewith for supplying power to the ignition circuit. Thetransistor oscillator has the great advantage of operating at a highfrequency as compared to vibrators thus reducing the size of transformerrequired.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein preferred embodiments of the present invention areclearly shown.

In the drawings:

The single figure drawing illustrates an electronic ignition circuitmade in accordance with this invention. Referring now to the drawing, itis seen that the power supply for the ignition circuit includes atransistor oscillator circuit generally designated by reference numeral10 and a storage battery 12. The storage battery in most passenger carsystems will be of twelve volts although it is apparent that thisvoltage will vary with different types of motor vehicle equipment. Oneside of the battery '12 is connected directly to ground as shown whereasthe opposite side thereof is connected with leads 14 and 16 through anignition switch 18.

The transistor oscillator circuit includes a pair of PNP transistors 20and 24, each having an emitter electrode e, a base electrode b and acollector electrode 0. The emitter electrodes of the transistors areconnected respectively with resistors 26 and 28 and the opposite ends ofthese resistors are connected to a junction 30. The junction 30 isconnected to a junction 32. The junction 32 is connected with lead 14which forms a common connection for junctions 30, 32 and 34. Thecollector electrodes of transistors 20 and 24 are connected withopposite sides of the primary winding 36 of a transformer that isgenerally designated by reference numeral 38. It is seen that thetransformer has a secondary winding 40 and a tertiary winding 42. Thesecondary winding has a greater number of turns than the primary toprovide a transformer that steps up the voltage from a primary tosecondary. The primary winding has a center tap 44 whereas the tertiarywinding has a center tap 46. The center tap 44 of primary winding 36 isconnected directly to ground through a ballast tube 48, whereasthe'centertap 46 of tertiary winding 42 is connected with junction 32.It is thus seen that the center tap of tertiary winding 42 is connectedwith the emitter electrodes of transistors 20 and 24 through resistors26 and 28. The base electrodes of transistors '20 and 24 are connectedwith opposite sides of tertiary wind ing 42 through resistors 50 and 52.A resistor 54 is con nected across the base and collector electrodes oftransistor 20. 7 v

The lead 16 that is connected to one side of ignition switch 18isconnected with a junction 56 through a starter switch 58 that controlsenergization of a starting motor designated by reference numeral 60. Thestarting motor, as is well'known to those skilled in the art, is used tocrank the engine during the time that it is desered to start the engine.The junction 56 is connected with a relay switch terminal 62 and isconnected to one side of a relay actuating coil 64. The opposite side ofthe actuating coil is connected directly to ground as shown. Theactuating coil 64 magnetically pulls the switch contactor 66 intoengagement with switch confactors 62, 68 and 70 against the bias ofspring 72 whenever the actuating coil 64 is energized. The switchcontact 70 is connected to one side of starting motor 60 whereas theopposite side of the starting motor is con nected directly to ground asshown. The switch contact 68 is connected to one side of a relayactuating coil 74 that magnetically controls the movement of a relayarmature designatetd by reference numeral 76. The opposite side ofactuating coil 74 is connected directly to ground and this relay alsomagnetically operates armature 78 whenever the coil 74 is energized. Thearmature 78 cooperates with switch contacts 83 and 84. The armature 76is normally held in contact with switch contact by a spring 85 whereasthe armature 78 is normally held in engagement with switch contact 84 bya spring 86. It thus will be apparent that whenever the actuating coil74 is energized, the armatures 76 and 78 will be moved to engagerespectively switch contacts 82 and 83. When a coil winding ,74 is notenergized, the relay armatures remain in the positions shown in thedrawing.

The relay contact 80 is connected to a center tap 88 of secondarywinding 40 whereas the relay contact 82 is connected to one side 90 ofsecondary winding 40. The relay contact 83 is connected to a tap point91 located intermediate the ends of a resistor 92 that is connectedbetween lead 93 and ground. The relay contact 84 is connected betweenlead 93 and ground. The relay contact 84 is connected to a second tappoint on resistor 92 as shown.

The output of the energizing circuit for energizing the primary winding95 of the ignition coil 96 is fed from the secondary winding 40 of thetransformer. Thus, one side of the trans-former secondary 40 isconnected with a junction 97 through a lead 98. The junction 97 isconnected with a lead 100 which is, in turn, connected to one side of ap-n junction semiconductor diode 102 which is, in this case, a silicondiode. The silicon diode is, as is well known to those skilled in theart, formed primarily of silicon material and has a junction formed of pand n type material. This diode is sometimes termed as a p-n junctiondiode or as a silicon junction diode. This type of diode has a very lowvoltage drop when conducting current in the forward direction and thisvoltage drop remains substantially constant with changes in current flowtherethrough. The junction 97 is connected with a second silicon diode104 and the opposite side of this diode is connected with a junction106. The junction 106 is connected with lead 108 through a third silicondiode 110 poled in such a direction as to prevent current flow towardjunction 106. The junction 106 is also connected with a condenser 112,the opposite side of which is connected with junction 114. A condenser116 is connected between junction 114 and ground as shown and thiscondenser is also connected to one side of silicon diode 102. Thejunction 114 is connected with the relay armature 76 by means of a lead118. It will be appreciated that the silicon diodes 104 and 102,together with the condensers 112 and 116 form a rectifying voltagedoubler circuit which is connected between one side of transformersecondary 40 and center tap 88 whenever the relay armature 76 is in theposition contacting switch contact 80. It will also be apparent that thevolt-age developed by this voltage doubler circuit from the transistoroscillator appears between lead 108 and ground and thus is available forsupplying current to the primary winding 95 of ignition coil 96. Theignition coil 96 has a secondary winding 120 which is connected betweenjunction 122 and spark gap 124 of spark plug 126.

The circuit for controlling the application of current to the primarywinding 95 of ignition coil 96 includes and inductance 128 and acondenser 130. It is seen that the inductance 128 and condenser 130 areconnected in series between lead 108 and ignition coil 95. Since oneside of the ignition coil 95 is grounded as shown, the inductance,condenser and primary winding of the ignition coil are connected inseries between lead 108 and ground. A gas filled thyratron tubedesignated by reference numeral 132 is connected between lead 134 andground. The grid 136 of thyratron tube 132 is connected with a resistor133 and with the secondary winding 140 of a transformer generallydesignated by reference numeral 142. The primary winding 144 of thetransformer is connected with junction 146 and with the relay armature78. The junction 146 is connected to ground through a set of breakercontracts 148 which are opened and closed by a cam 150 that is driven insynchronism with the engine of the motor vehicle as is well known tothose skilled in the art. A second gas filled thyratron tube 152 havinga grid 154 is connected between lead 134 and ground. A condenser 156 isconnected between the grid of tube 152 and ground.

In operation, when it is desired to start the motor vehicle engine, theswitches 18 and 58 are closed to energize both the ignition circuit andthe starting motor circuit. The closure of switch 58 completes a circuitto ground for relay coil 64, thus shorting together contacts 62, 68 and70 by the movement of switch contactor 66. With these contacts shorted,a circuit is complete for the starting motor 60 to ground through switchcontacts 62 and 70. In addition, the relay coil 74 is energized throughswitch contacts 62 and 68 to move the armatures 76 and 78 to positionscontacting respectively switch contacts 82 and 83. The movement of relayarmatures 76 and 78 from their normal positions applies a greaterpotential developed across a portion of resistor 92 to the primarywinding of transformer 142, and also applies the voltage developed bythe entire secondary winding 40 to the ignition circuit. Thisarrangement is desirable since the output voltage of storage battery 12will drop when the starting motor load is connected thereto and themovement of armatures 76 and 78 thus compensate for this drop in voltageby applying greater voltages to the ignition circuit.

The closure of ignition switch 18 connects one side of battery 12 withthe emitter electrodesof transistors 20 and 24 through resistors 26 and28. When this occurs, the transistor 20 will begin to conduct currentfrom emitter to collector. This current will pass from battery 12through lead 14, through the emitter to collector circuit of transistor20, through a portion of the primary winding 36 and thence throughballast tube 48 to ground. The current flowing through one half of theprimary winding allows flux to be built up into the core of transformer.33. This current grows at a rate determined by the total circuitresistance and self-inductance of one half of the primary winding. Theflux in the core of transformer 38 is accompanied by a correspondingvoltage in the tertiary winding 42 of the transformer. This voltagecauses the transistor 20 that was conducting to be turned off and turnson the transistor 24. When the transistor 24 has been renderedconducting, current is allowed to flow through its half of primarywinding 36. The build up of current and voltage is again a time functionof the same circuit parameters, resistance and coil primary inductance.When the current on the second side of the primary winding 36 hasreached a predetermined value, the tertiary winding shuts off thetransistor 24 and brings the transistor 20 into conduction again. Inthis way, the transistor oscillator operates as a self-excited generatorof alternating current which may have a frequency in a neighborhood of20,000 cycles per second.

The voltage applied to the ignition circuit will either be the voltageappearing across the entire secondary winding 4'0 which occurs duringstarting of the engine or will be the voltage appearing across the tappoint 88 and one side of the secondary winding 40 during the time thatthe engine is running and when the starting motor is not energized. Ineither case, the A.C. voltage is rectified by silicon diodes 104 and 102and thus appears as direct current voltage between lead 108 and ground.

The D.C. voltage appearing between lead 108 and ground is operative toforce current through inductance 128, condenser 130 and through primarywinding of the ignition coil to ground. The condenser will thus build upa charge of the polarity indicated in the drawing. During the time thatthe breaker contacts 148 were closed, current is permitted to flowthrough the primary winding 144 of the transformer 142 via a circuitthat may be traced from junction 34 through lead 93 through all or apart of resistor 92, through armature 78 and thence through the primarywinding 144 to ground, through breaker contacts 148.

When the breaker contacts 148 open, a high voltage is induced in thesecondary winding of transformer 142 and this voltage is applied to thegrid of tube 132 through resistor 138. This voltage is of such apolarityas to cause conduction of tube 132. With tube 132 conducting,the condenser 130 discharges through a circuit that include tube 132 andprimary winding 95. The discharging of condenser 130 through primarywinding 95 causes a high voltage to be developed in secondary winding120 which is applied across spark gap 124 to cause the firing of sparkplug 126. The discharging circuit for the spark plug includes both theprimary and secondary windings of the ignition coil 96. It will beappreciated, of course, that the secondary winding 12% will be connectedwith a plurality of spark plugs through a distributor mechanism notshown.

The tube 152 is used to drain otf-the residual charge that appearsacross condenser 130 after it discharges. Thus, after the condenserdischarges, it builds up a small charge that is opposite in polarity tothat indicated in the drawing and this charge is drained off by tube152. It is noted that the tubes 132 and 152 conduct current in oppositedirection between lead 134 and ground and, thus, the tube 152 isefiective to drain off this residual charge but will not permitdischarging of condenser 130 during the time that it has the polarityshown in the drawing.

While the embodiments of the present invention as herein disclosedconstitute preferred forms, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. An ignition circuit for an internal combustion engine, comprising: asource of direct current voltage, an oscillator circuit including atleast one transistor, means connecting said oscillator circuit with saidvoltage source to be energized thereby, a p-n junction semi-conductorrectifier, means connecting the output terminals of said oscillatorcircuit with an ignition coil energizing circuit through said rectifier,an ignition coil having a primary winding and a secondary winding, meansconnecting the primary winding of said ignition coil in circuit withsaid energizing circuit, and means including an electronic switch forcontrolling the energization of the primary winding of said ignitioncoil from said energizing circuit.

2. An ignition circuit for an internal combustion engine, comprising: asource of direct current voltage, an oscillator circuit including a pairof transistors having output terminals and connected to be energized bysaid source of direct current voltage, an ignition coil energizingcircuit, a voltage doubler circuit including a pair of condensers and apair of p-n junction semiconductor diodes, means connecting the outputterminals of said oscillator circuit with said energizing circuitthrough said conductor diode, and means including said breaker contactsand electronic switch means for controlling the energization of theprimary winding of said ignition coil from said energizing circuit.

3. An ignition circuit for an internal combustion engine, comprising; asource of direct current voltage, an oscillator circuit includingat-least one transistor, means connecting sa'd oscillator circuit to beenergized from said source of direct current voltage, an ignition coilenergizing circuit, a p-n junction semiconductor rectifier, meansconnecting said energizing circuit with said oscillator circuit throughsaid rectifier, an ignition coil having a primary winding and asecondary winding, means connecting the primary winding of said ignitioncoil to be energized by said ignition coil energizing circuit, and meansfor controlling the application of power tosaid primary winding fromsaid ignition coil energizing circuit.

4. An ignition circuit for an internal combustion engine, comprising, asource of direct current voltage, an oscillator circuit including atleast one transistor, means connecting said oscillator circuit to beenergized from said source of direct current voltage, an ignition coilenergizing circuit, a rectifier, means connecting said en ergizingcircuit with said oscillator circuit through said rectifier, an ignitioncoil having a primary Winding and a secondary winding, means connectingthe primary winding of said ignition coil to be energized by saidignition coil energizing circuit, and means including a condenser andelectronic switch means for controlling the application of power to saidprimary winding from said ignition coil energizing circuit.

References Cited in the file of this patent UNITED STATES PATENTS2,536,143 Short Ian. 2, 1951 2,826,731 Paynter Mar. 11, 1958 2,836,787Seider May 27, 1958 2,837,651 Schultz June 3, 1958

